Exhaust emission control devices, such as catalytic converters, achieve higher emission reduction after reaching a predetermined operating temperature. Thus, to lower vehicle emissions, various methods are possible to raise emission control device temperature as fast as possible.
In one approach to raise the emission control device temperature, an engine is operated with a rich air-fuel ratio and secondary air is directly introduced into the exhaust upstream of an emission control device. Such a system is disclosed in U.S. Pat. No. 5,136,842. In this system, the excess fuel from the engine is expelled into the exhaust, where it reacts with the secondary air upstream of the emission control device. The reacted fuel increases the temperature of the exhaust, thus heating the emission control device. However, in order to introduce the secondary air into the exhaust, a secondary air pump is used to increase the pressure of the secondary above the exhaust pressure. Use of such a pump may degrade fuel efficiency and requires additional packaging space, thus reducing the efficiency of the engine.
The inventors herein have recognized the issues with the above approach and offer a method to at least partly address them. In one embodiment, a method for a turbocharged engine comprises during an engine cold-start, delivering boosted air from downstream of a compressor into a wastegate duct coupled across a turbine and exothermically reacting a reductant with the boosted air upstream of an exhaust emission control device.
In this way, boosted air downstream of the compressor may be directed to the exhaust upstream of an emission control device without utilizing a separate pump. By utilizing the pressure differential between the throttle inlet pressure downstream of the compressor and the turbine outlet pressure near where the secondary air is introduced into the wastegate valve, the boosted air may be driven to the exhaust without a separate pressurization mechanism. Further, in some examples the wastegate valve, which regulates the amount of exhaust bypassing the turbine via the wastegate duct, may be used to control the reaction rate between the exhaust and the introduced boosted air.
The present disclosure may offer several advantages. For example, by relying on boosted air rather than air pressurized by a pump, a separate air pump may be dispensed with, thus improving engine efficiency. Additionally, by introducing the boosted air to the wastegate duct, the reaction between the reductants in the exhaust and the boosted air may be controlled by the wastegate valve, thus ensuring that the turbine, emission control device, or other exhaust system components are not subject to high temperatures that may result in component degradation.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.